1. Field of the Invention
This invention relates to a process for deasphalting an asphalt-containing mineral oil. More particularly, this invention relates to contacting an asphalt-containing heavy petroleum oil feed with a liquid hydrogen sulfide deasphalting solvent for a time sufficient to separate a substantial portion of the asphalt from the oil.
2. Description of the Prior Art
The residual fraction or residuum resulting from atmospheric or vacuum distillation of crude oil contains high viscosity, high boiling point petroleum oil fractions useful for heavy duty lubricants for tractors, automotive, automobile and aircraft services, etc. These relatively heavy, high viscosity fractions are also useful as cracking feeds for the production of lighter, lower boiling lube and fuel components. However, in order to produce useful lube or cracker stocks from residuum, the asphaltenes must first be removed therefrom. These asphaltenes are black, solid substances at room temperature and contain most of the metals and sulfur present in the residuum. The asphalt produced from the residuum can be blended with lighter components into relatively heavy fuel oil stocks, can be used as a coking aid in various refinery coking processes, can be sold as is or can be air blown or oxidized to produce asphalt of improved flexibility, greater resistance to weathering and decreased brittleness which is useful for the production of roofing and road materials.
Solvent deasphalting of residuum is well known in the art and many solvents and solvent combinations have been suggested and used for the deasphalting thereof. Most commonly, nonpolar, light hydrocarbon solvents containing 3 to 8 carbon atoms in the molecule such as propane, propylene, butene, butane, pentene, pentane, hexane, heptane and mixtures thereof are used alone or in admixture with other solvents such as ketones, liquid SO.sub.2, and esters. Typical of prior art deasphalting processes is the process described in U.S. Pat. No. 2,337,448 in which a heavy residuum is deasphalted by contacting it at elevated temperature with a deasphalting solvent such as ethane, ethylene, propane, propylene, butane, butylene, isobutane, and mixtures thereof. Other solvents may be used in the process of this patent such as pentane, gasoline, mixtures of alcohol and ether, acetone and other solvents capable of dissolving the oil but not the asphaltenes. Most commonly, propane is used in deasphalting operations. However, propane deasphalting is somewhat limited in that it will extract only about 40 to 60% of a petroleum residuum and the bottom fraction resulting from propane deasphalting, and mounting to about half of the residuum, is unsuitable for use except as an ingredient in the blending and production of heavy fuel oils. Additional refining treatments must be employed in order to precipitate therefrom additional asphalt and to release more useful deasphalted oil from this bottoms fraction. Generally, the higher molecular weight aliphatic hydrocarbons such as pentane, hexane and heptane will result in a greater yield of deasphalted oil and produce asphalt with a higher softening point.
However, as one uses solvent of increasing molecular weight and/or boiling point, one loses the advantage of facile stripping under mild conditions obtainable with the autorefrigerant hydrocarbons such as propane.